This invention relates to a method of subaqueous pile driving, in which the pile and pile hammer are brought under water. Such a method is known. With said known method, firstly a guide pile is positioned on the ground which projects above the water-level and the pile to be driven as well as the pile hammer are guided along said pile. Such a method is complicated and is more difficult and more expensive as the depth of water increases.
It is an object of the invention to provide a method and appertaining device with which pile driving under water is made possible in a simple manner.
In accordance with the invention, said object is achieved in that the pile at the top is suspended on one or more cables in such a manner that in any case at least two cable sections run upwards from the top of the pile, parallel to each other, towards a device above water-level, by means of which the pile can be lowered by the cables onto the ocean floor and for the process of lowering the pile hammer is positioned on the top or head of the pile and is lowered along with the pile, in which the pile hammer is guided on the cable sections. In accordance with the invention use is no longer made of a guide pile but the pile and pile hammer are suspended on one or more cables and the whole assembly is lowered with the lower end of the pile facing the region where the pile will be driven into the ground. If required, the pile point may be steered by means of easily detachable cables secured near the point, e.g. when due to currents there is some difficulty in directing the pile point. During lowering, the cables take care that the sometimes top-heavy assembly of pile and pile hammer does not tilt.
If for some reasons the process of pile driving has to be interrupted and the ram has to be raised, it may be guided back along the cables to the pile head.
If the pile point has reached the ocean floor and the point has penetrated into the ground preferably by virtue of its own weight and the weight of the ram, pile driving may begin. Use is made of the flexibility of the, if required, already lowered cable or cables, which, of course, are lowered further after each blow, in which certainly at the beginning the value of the tension in the cables is kept such that the pile and pile hammer can be kept upright. Such tension may be less than the tension resulting from the proper weight of pile and pile hammer.
At the beginning, one has to be careful when driving the pile but this is no problem inasmuch as it can be controlled with a pile hammer of the type known from Dutch Pat. No. 137,548.
The lower end of the pile is preferably provided with a temporary support, said support enlarging the base and having a slidable frictional contact with the pile. The stability of the pile is thus increased. Said support has a connection with the pile of a kind that during pile driving the pile will slide through said support until the pile driving device has reached the support device. Said support device should then be removed but it may also be a structure which can be demolished by the pile driving apparatus.
The invention also relates to a device for applying the method and said device comprises a bearing element to which the pile head may be secured and to which the cable or cables may be connected, a pile hammer, said hammer being provided with means for guiding the cable sections therethrough, as well as lifting means above the water-level for carrying, lowering and hoisting the cable and the pile hammer. Said bearing element may consist of a clamping device on the top or head of the pile and fastenings for cables running towards a lifting device. The pile hammer is suspended in a known manner on another lifting device.
If the ground is very soft, the afore-mentioned support device cannot be used. Due to the fact that the pile does not encounter much resistance in the soft ground, the cable or cables acting as bearers of the pile will have to take considerable blows, which is undesirable.
It is the object of the invention to provide also a solution for this problem and this is achieved in that the means of the pile hammer for guiding the cable or cables of the pile are constituted by a long framework, wherein the pile hammer and the pile are guided freely slidable in a vertical direction, said framework being secured to the lifting means for the pile hammer. If the frame is suspended on its hoisting cable and one creates a slack in the carrying cables of the pile and, thus, takes away partly or completely the stabilizing effect of said carrying cables on the position of the pile, said guide frame partly or fully takes over the stabilizing function, as a result of which, depending on the circumstances, the loads which would occur otherwise in the carrying cables can be considerably reduced and/or fully neutralized.
In accordance with the invention the bearing element may also be provided with cable discs for guiding a through cable, one end of said cable being secured to a stationary point of the lifting means and the other end being secured to the movable portion of the lifting means. The principle of the pulley-block is thus, advantageously applied. If the principle of the pulley-block is applied with a singular, the cable discs should be disposed on either side of the pile in a vertical mid-section of same and the pile is provided with a transverse bore through which the cable is guided. If the principle of lifting is carried out in duplicate by passing the cable over a cable disc on the lifting device and by having the cable run back over a second pair of discs near the pile head, then four discs are needed which may be located at such distances from each other and in such a manner relatively to the pile that no transverse bores are needed, but the cable sections are guided along the sides of the pile. This is also the case when the principle of single lifting is applied with two parallel cables.